Internal combustion engines generate heat during operation that is released into the environment through exhaust gas emissions. Modern emission controls systems may utilize energy, in the form of heat from the exhaust gas, to operate various components, for example, Diesel Particulate Filters (DPF). In other cases, heat may be undesirable and removed by use of other components and systems.
One example of a case where additional heat is desirable for the operation of an engine is the operation of a DPF, which depends on a reaction that occurs internally to the DPF and burns particulates that have accumulated therein. Some engines incorporate thermal shielding on their exhaust systems to contain exhaust heat and make it available for emissions components. Heat makes the regeneration of the DPF more efficient. One example of a case where removal of heat is required for proper operation of the engine is in an exhaust gas recirculation (EGR) system, which recirculates cooled exhaust gas into an intake of the engine. EGR systems typically use exhaust gas coolers to remove heat from an exhaust gas stream during recirculation.
Even though heat input may be desirable for some engine systems, heat removed from other systems that is typically rejected back to the engine is undesirable. Heat rejected and/or generated internally to the engine is removed from the engine by a cooling system. Typical cooling systems promote efficient operation of the engine and protect heat sensitive systems. Thermally conductive fluids, that include for instance oil or engine coolant, carry heat collected from within the engine and/or engine components to a radiator, which then expels the heat to the environment.
Exhaust gases from internal combustion engines can typically contain hydrocarbons (HC), Carbon Monoxide (CO), and particulate matter (PM). Oxidation catalysts, typically comprising a platinum group metal dispersed on a refractory metal oxide support are known for use in treating exhaust gases to remove these pollutants by catalyzing the oxidation of these pollutants to carbon dioxide and water.
In EGR systems, HC and PM can precipitate out of exhaust gases and collect on surfaces of EGR system components such as coolers, valves, and pipes, and on down stream systems, such as intake manifolds, intake ports, and intake valves. EGR Coolers may become “fouled” as a result and lose heat transfer effectiveness and flow area. EGR valves can become fouled with deposits and become inoperable or sluggish. Deposits in downstream systems can also change their intended characteristics, or performance. As such, reduction of HC and PM in the EGR system is desirable. Some EGR system designs, therefore, incorporate an oxidation catalyst upstream of the EGR cooler and valve, advantageously removing some of the HC and PM.
A disadvantage of this approach is that the catalytic oxidation of pollutants in the EGR exhaust stream releases heat. This additional heat load must be compensated for by the EGR cooler and vehicle radiator.